Television receiver



TELEVISION RECEIVER Filed Dec. 15, 1939 Inventor Robert, B. D me, y W 6.)

His Attorney.

Patented Sept. 9, 1941 TELEVISION RECEIVER Robert B. Dome, Bridgeport, Comb, asslgnor to General Electric Company, a corporation of New York Application December 15, 1939, Serial s... 309,443

(or. ire-1.5)

11 Claims.

My invention relates to television receivers and more particularly to means for controlling the background brilliance of the reproduced picture.

It has for one, of its objects to provide improved means to control the background brilliance of the reproduced picture in accordance with the background brilliance of the transmitted picture as represented by the intensity of the picture signal currents as received in the receiver.

In my copending application Serial No. 243,134 filed November 30, 1938 and entitled Automatic background control for television systems, I have illustrated a system in which the background brilliance of the reproduced picture is controlled in accordance with a unidirectional electromotive force produced by rectification of the television picture signal, this rectification occurring in the grid circuit of an amplifier of the television signals. That system possesses the advantage that the cathode of the picture reproducing device is maintained substantially at the potential of the cathode of the picture signal amplifier whereby the heaters ior these cathodes may be energized from the same source and a minimum of insulation between the cathode and heater of the picture reproducing device is therefore required.

My present invention has for another of its objects substantially to retain this advantage, and at the same time to secure improved operation and reduced cost of the system.

A particular object of my invention is so to arrange the circuits as to reduce the cost of the equipment necessary to supply the high voltage operating potential for the'picture reproducing discharge device.

Still another object of the invention is to provide improved means to prevent damage to the is shown,rbut which receives the television modulated carrier wave, demodulates it, and supplies the reproduced television picture signal electromotive force between terminals l0 and II shown on the drawing. This electromotive force, representing the transmitted picture is supplied through a coupling condenser I! to a control electrode l3 provided in an electron discharge amplifier ll.

This electromotive force has alternating current intensity variations therein which arein accordance with the gradations of shade of an element of area of the picture transmitted as said element is scanned over the picture. vThese variations I shall refer to as the picture signal. It also has a certain average, or overall, intensity which is dependent upon the overall, or back-r ground, brilliance of the picture.

The grid circuit of the device It is provided with the grid condenser l2 and a grid leak l2.

This leak I2 is connected, for direct current, across the condenser I2 through apparatus. not shown, which is connected to terminals Ill and I I, so asto provide a discharge path for the condenser. This grid leak and condenser combination I2, I! has such a time constant that upon occurrence of rectification in the grid circuit of the discharge device H a unidirectional potential is produced upon resistance I! having a magnitude, which is dependent upon the background,

or overall, brilliance of the transmitted picture. This electromotive force is utilized in the manner presently to be described to control the brilliance of the reproduced picture.

The discharge device It has acathode ii, an

cathode ray screen during the heating up period of the cathodes of the system before the deflection potentials are applied to the deflection system of the picture reproducing device.

The novel featureswhich I believe to be characteristic of my invention are set forth with particularity inthe appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by, reference to the following description taken in connection with the accompanying drawing in which Fig. 1 represents an embodiment of my invention, and Figs. 2 and 3 represent modifications thereof.

Referring more particularly to Fig. 1 of the drawing, my invention is illustrated as e bodied anode l6 and a suppressor grid l'l, all connected in a conventional manner to amplify the picture signals supplied to the grid l3 thereof. The anode I6 is supplied with operating potential from the power supply rectifier l8 of the television receiver through a resistor IS. The device i 4, likewise, has a screen grid 20 which is supplied with operating potential from the rectifier l8 through a resistor 2|. The rectifier l8 alsozsupplies operating potential for other discharge devices of the television receiver through conductor 22 and ground.

The picture signal output of the-amplification stage id is developed upon resistance is and is supplied through a coupling condenser 23 to a control electrode 24 provided in a pict'urereproducing cathode ray device 25 thereby to control the intensity of the cathode ray in that device. The picture reproducing device 25 has a cathode in a television receiver, only a portion of which 26, which is connected to the movable contact 2! rectifier it, if desired.

oi a potentiometer ll. connected across the output oi the power supply rectifier ll.

The biasing circuit for the control electrode 24 oi the picture .reproducing 2" is completed through a resistor ii to the Junction between a pair of resistors 82 and 33, which are connected in series-between the left-hand terminal or the resistor 2| and the negative terminal or the potential source II. The upper terminal or the resistor 82. and hence the screen grid oi'device It, is maintained at ground potential for currents or signal irequency by condenser 84. which is connected between the upper terminal of the resistor 32 and ground. In similar manner,-a by-pass condenser II maintains the cathode It at ground potential for alternating currents.

The picture tube II is provided with a first, or acceleration, anode "and a second anode II, the latter being connected to the positive terminal of a source It or relatively greater potential than that or source It, and which may comprise a second power supplyrectifler connected across a resistance 38 as indicated by the and signs on the drawing. The negative terminal ot'this source I! is connected to the positive terminal or the potential source It and to the acceleration anode it, the potentials of the source It and 30 thus being applied in aiding relation between the cathode and the anode 31 of the picture reproducing device 28. 1

The heaters ll and 44 for the cathodeso! the various discharge devices are shown connected to the same energization circuit 43.- The heat- .ers of the cathodes of other discharge devices in the receiver may also be heated from this same circuit through conductors 41. This may include the discharge devices which generate the scan? ning, or deflection, potentials for the cathode.

ray device. Any or the heaters may, or course, be supplied through individual circuits from separate secondary windings on a common transformer such as that which supplies potential to The discharge'devices or the'receiver, which generate 'thescanning potentials for device; II,

I since they usually have indirectly heated cathodes, are inoperative to produce. the'scanning, or

l deflection, potentials u'ntii'their cathodes have had time to become proper y heated after the receiver is initially energized. This condition necessitates the use or means, which will'be presently described, to protect the screen of the oath ode ray-device from injury due to impingement or the beam thereon'during this initial heating period after the receiver energizing circuits have been energized.

The picture reproducing device 25 is also pro-. vided either with deflection electrodes, or deflece tion coils, not'shown, which are energized from the scanning circuits of the television receiver. Such systems are entirely conventional and oper- .energization or the cathode of rectifler II, which commonly is or filamentary type, as when power is iirst applied to the television receiver. and becomes energised only alter the cathode of the various discharge devices energised thereby have had time to heat up so that current flows from the rectifier. This means that in the event that the cathode of the picture reproducing device 2| becomes eii'ective to emit the cathode ray prior to application of scanning potentials to the deflection system or thiadevice the ray is not focused =upon the screen, but falls upon sucha large areathereof that it is insuilicientiy intense at any point to produce injury to the screen. After the cathodes oi the discharge devices of the receiver become heated, and current flows irom the rectifier, focusing coil 40 becomes energized and the ray is focused upon the screen. By

7 device draws maximum anode and screen grid ate in the usual way'to deflect the cathode ray of the picture reproducing device 25 across the screen or that device in sucha fashion that when modulated .by the control electrode 24, it reproduces thetransmitted pictureuponthe cathode ray screen.

The picture reproducing device is also provided with a focusing coil 48 the' function 01' which, when energized, is to focus the cathode ray upon a small area, or spot, on the screen. 'I'his'coil is connected, however, in the negative return lead or rectifier It; that is, between ground at Ii and the anodes of the .electron discharge rectifier of the television picture.

42, so that it is not energized upon initial 7 current. The screen grid current, in flowing through .the resistor 2|, produces a voltage drop across this resistor thereby to establish a predetermined voltage drop across the resistors 32 and 33, which are'connected in the biasing circuit of the control electrode 24 or the picture reproduc 1 v ing device 2'.

The control electrode 24 is biased by the diflerence in the potentials appearing across resistor 38 and that appearing across the lower portion of potentiometer 2. below the movable contact 21. these potentials being in opposed relation. Under the condition that no picture signals are present at the input terminals II, II, the movable contact "is adjusted along the potentiometer 21 to a point where the control electrode 2t or the picture reproducing device II -'is just biased'to cutofl'. The fluorescent screen 01' the picture reproducing device is then dark; as is proper for a black picture.

Now assume that a picture signal is supplied to the input terminals M, II corresponding to a picture composed of light and dark areas. The control electrode II of the device it becomes positive during a portion or each alternating current cycle of the picture signal and rectification or the signal between the control electrode II and the cathode l5 ensues thereby charging condenser It, as in ordinary grid leak and condenser rectific'ation, until the control electrode is biased negatively in proportion to the maximum change in the picture signal caused by the lighter areas This'ch'ahge in the bias or the control electrode II is thus dependent upon an integrated change in the picture signal produced by gradations oi light intensities between: the li ht and dark areas or the picture and thus vitcorresponds with the overall brilliance oi the televised picture.

As the control electrode I3 is biased more negatively by rectification or the picture signal, the anodevand screen gridcurrents are thereby ponent of the television signal.

" that the overall brilliance of the televised picture controls the bias of the control electrode 13 of the device l4 and by controlling the screen grid current. of this device, directly controls .the bias of the control electrode 24 thereby automatically to control the overall brilliance of the picture reproduced on the fluorescent screen the picture reproducing device. r

It has been found advisable for best operation tochoosea value for the resistors 32 and 33 such that the same change of potential drop occurs across the resistor 33 as occurs across the resistor l9 with changes. in the overall brilliance of ,the' televised picture. In this way, the amvision signal applied to the control electrode 24 is the same as theampliflcation, or. gain of this device for the direct current or background com- Thus these two components of the received signal as applied to the cathode ray device are maintained in their proper relationship to each other. By proper choice of resistors 32 and 33 with respect to each other to increase, or decrease,

' I 3 00.485 In one embodiment oi my invention the circuit These values are given merely by way of exelements have the following values:

Resistance 32 .megohms 2.2 Resistance 33...... ...'..do 1 Resistance 21---. ....ohms 56,000 Resistance 28"-. do 10,000 Resistance 19 do 1,800 Resistance 31,. Zero Capacity 34 microiarad -25 Capacity 23 do I .25

ample and may vary widely in difierent installations. They are not intended as any limitation of my invention. a

Fig. 2 represents a modification of my inventionin which the lower terminal of resistance pliflcation, or gain of device l4, for the aiternating current, or picture, component of the tele the voltage on resistance 33 the background changes maybe exaggerated, or they may be made subnormal in amount as desired, thereby to produce special eflects as desired. In this way, compensation may bev effected for attenuation of background signal in the system prior to discharge device l4. v

a It has been found in practice that with the system constructed in accordance with my invention the cathode 29 of the pictureyreproducing device maybe operated near the potential 01'' the cathode of device i4 and near ground. This enables the picture reproducing device to constructed with a minimum of insulation between its heater element 44 and the cathode 26. The heater 44 may thus be heated by the same source of heating energy asis used to heat the cathode heater of. the discharge device [4, as shown, or if energized from separate windings of a transformer, for example, it renders possible a reduction in cost of theinsulation necessarilyprovided to insulate such winding from each other and from ground.

' An additional advantage'of my invention resides in thefact that the potential sources 39 and it may be connected in series between the cathode l5 and the anode' 31' of the picture reproducing device. With the potential sources 39 and" connected as shown, the bleeder're- .sistor 39 across the anode source 39 can be dis--v pensed with, or a much higher resistance, such as 20 megohms, employed since it is not necessary to provide a tap connection from any such bleederflt'o any electrode such as. the anode 36 and 'it isnot necessary that such resistance carry any great amount of current. This produces a saving in thepower required from the source 28 is connected to ground through diode 45. When so connected, during the initial heating up period of diode 45, the cathode of which may be energized from circuit 43 otFig. 1, resistance 28, and hence the cathode26 of device '25 is' at the full'potential of the rectifier J8." The grid of this device is maintained near ground potential through resistance '33 and hence it is highly negative relative to its cathode. This prevents the cathode ray from impinging upon the screen-:until such time as the deflection potentials are applied and the cathode of diode 45 has'become heated. In this way the connection of the focusingcoil 46111 the negative lead of rectifier l8, as shown in Fig. 1, may be obviated. Fig. 3 is similar to Fig. 1 but-diflers therefrom in that the lower terminals of resistances 28 and 33 are connected,.not to ground as in Fig.- l; but to a point 500i potential negative with respect to ground. Thenegative side of the rectifier I8 is, in, this case, connected to ground.

through a resistance 5| upon which a potential develops which is negative with respect to ground.

This means that the tap 21, and hence the catl'r-fl the appended claims to cover all such modifications as fall within the true spirit and scope'oi my invention. I V v a What I claim as new and desire to secure by Letters Patent of the United States is;

1. The combination. in atelevision receiver,

of a cathode ray picture reproducing device having a cathode and a control electrode, an amplifler having ananode circuit, a screen grid cir-' cuit, and acontrol grid circuit, means to supply to said control grid circuit signal currents representing the transmitted picture and its background brilliance, means todevelop in saidanode, circuit electromotive force representing the transmitted picture and to supply said electromotive force between said control electrode and cathode of said picture reproducing device, means to de-;

velop in said screen grid circuit by reason ,of

current. flowing between said screen and cathode an electromotive force representing the background brilliance of said picture, and means to supply such electromotive force between the cathode and control electrode of said cathode ray device. a

2. The combination, in a television receiver,

fier having an anode, a screen grid, a control grid, and a cathode, means to supply between said cathode and control grid oi said amplifierv picture signals. and background signals, means to develop on said anode potentials representing said picture signals, and on said screen grid in response to current flowing between said" screen grid and'cathode potentials representing said background signals, means to supply a normal operating bias potential between the control electrode and cathode of said picture reproducing cordance with the potential on said screenv grid, and means to supply said potentials representing said picture signals from control electrode.

3. The combination, in a television receiver, of an amplifier including a cathode, an electron-' receiving electrode and an anode, a resistance connected between said cathode and electronreceiving electrode, a source of operating potential connected through a second resistance both between said cathode and electron receiving electrode and across said first resistance, whereby the potentialon said first resistance increases and decreases as current in said electron-receiving electrodeand said second resistance decreases and-increases. a cathoderay picture reproducing device having a cathode connected to a point on said source and a control electrode connected to an intermediate point on said first resistance, said points being such as to provide" oper ating bias potential between said cathode and control electrode of said cathode my device,-

said anode to said accuse turesignalcurrentsbetweensaidcathodeand' one of said outmitjclectrodes, means to supply alternating picture signals and unipotential background signals to sjaid electrode whereby said upon said resistance connected to one output electrode and the picturelsignals appear upon the other oivsaid resistors. in electron. discharge picture reproducing'device connected to e pond to ma picture and signals. appearing on said resistors, and rneanswhereby the amplification of said amplifier for said picture signals is,

substantiallyjequal to that for said ba ground device, means to vary said bias potential'in acsisnala 1 @a: an amplifier a cathodefa' control elecoi. 'operatin'g'potential connected between said cathode and-each. not said output electrodes, through respective resistors, a by-pass tor picture signal currents betvireenvsaid cathode and one 01 said outputelectrodes,- means to supply alternating. picture 'signalsand'unipotential background said control. electrode whereby said background signals appear upon said resistance connectedito said one output electrode and the picture signals appear upon the other of said resistor s,- anelectrondischarge picture reproducing device, connected to respond: to said 9101171126 and background signals appearing on said was r .e v

' "I. The" combination-{ins television receiver,

of a picture signal. amplifier having a cathode.

' an. electron receiving electrode T and a picture signal output, an electron discharge picture re- 1 producing-' devicei a cathode, a control means to transmit picture signals through said" amplifier and from said anode thereoi'to' the control electrode of said plcturereproducing de-' a vice thereby to reproduce the transmittedpic ture, and means to control the current in said electron-receiving electrode thereby to vary. the

potential on said first resistance and on said trol electrode or said cathode ray device to coni .trol the background brilliance or said picture.

4. The combination, in 'a television "recei v"er,=- oi' an amplifier having ;a cathode, an anode and an electron receiving screen electrode interposed" 1 therebetween, a source of operating potential :i'orq said electron-receiving electrode-v and anode, a

resistance path across said source, an electron discharge picture reproducing device having a' cathodeconnected to an-intermediate point on said source, and a control electrode connected ior low frequency and unidirectional currents to an intermediate point on saidmthi means to transmit signals representing'saidjpicturei through said amplifier and to vproduce.tinsaid anode voltages of. high frequency said picture and on said screen electrode'volt-v .age of low frequency varying with the background brilliance oi=said picture whereby the bias on a the control electrode or said picture reproducing deviceisv ried in'faccordance vwith the. 5mmelectrode, anaccele'ration anode and a high potential 'anode; j a 1 source of operating potential having its' Ipo sitive .".termina1-connected to said acceleration 1 and to said electron receiving electrode pointsatlow botentiai thereon on e t d? sn ctli e r o the cathode of s amplifier; and thercathode oi's'aid picture repro- 'ducing devices path acrou said source intermediate points. thereon connected for unidirectional' and low frequency currents to said electron electrode and to said cont l0 1' electrode r espectively, means to vary the currentfin d; e le c'tronreceiving electrode in accordan background signals, said resistance PC 1 8, O. proportioned that the potential said control electrode varies sum- 'ciently in. to changcsin current in said electron receiving electrode to control the backg'round briliiance;oi;the r produced picture, a 1 coupling 10! pictureLsignals between said. Pic .tur'e-; s ignal ;.output and control electrode,

1 a source oi; operating; potential connected -"betweenisaid acceleration anode and high potentialfelectrodewherebyjsaid cathodes are mainstained neanthe' samerpatennarma sources are utilized inserie's', and botH pIcture signals and backgroundjs'ignals are derived i'romsaid ampliground brilliance of said picture, and a high ire quency coupling forpicture signals between .said' anode and the control electrode oijsaid. picture H r A v discharge picture reproducing'devicehaving a cathode, a'control electrode, an'acceleration electrodeiand a high'potentiaranode, a source of reproducing device.

oi an amplifier'having 'a cathode, a control elcc'-.

8 The 1combiiiia ition,-in'- a i-television receiver, of a' icturev-signalf-amplifier having a cathode. an anode, and. .a screen electrode, anelectron trode, and a pair'oi output electrodes; a. source I perating poten ial hsvingitspositive termi- [of operating potential connec ed me l said 1 cathode and each or said-,outputelectrodes through respective. resistors, a by pa se- 1'01"pic 1 r al connected to said acceleration electrode, to saidganode gotsaid jamplifier fandithrough a reiisistance to; saidscreen electrode, and having to vary the current in said screen electrode and 5 in said resistance in accordance with background signals thereby varying the voltage on said screen electrode, and means'to supply a portion of the unidirectional voltage variation existing between said screen electrode and cathode of said amplifier between said control electrode and cathode of said picture reproducing device thereby to control the background brilliance ofthe reproduced picture, whereby both picture signals and background signals are supplied from said amplifierand 'both of said cathodes are at low potential.

9. The combination, in a television receiver,

of an amplifier having an anode, a cathode, a

control electrode, and a screen electrode, an electron discharge picture reproducing device having a cathode, a control electrode, an acceleration anode, and a high potential electrode, a source of operating potential connected between the anode and cathode of said amplifier, the

positive terminal 01 said source being connected to said acceleration anode and an intermediate point. thereof being connectedto the cathode of said picture reproducing device, a resistance path across said source, said screen grid and said control electrode of said picture reproducing device being connected to intermediate points on said path whereby the potential on said control electrode varies responsively to current variations in said screen electrode, an additional source of operating potential connected between said acceleration anode and high potential electrode, a coupling for picture signals between the anode oi. said amplifier and the control electrode of said picture reproducing device, and means to supply alternating picture signals and unidirectional background signals to the control electrode of said amplifier.

10. The combination, in a television receiver, oi an amplifier having a cathode and an electron receiving electrode, a picture reproducing device having a cathode, a control electrode, and an anode, a source of potential connected between said cathode of said amplifier and anode of said picture reproducing device, two shunts across said source, said electron-receiving electrode and control electrode-being connected to intermediate points on one of, said shunts and said cathode of said reproducing device being connected to intermediate low potential points on the other of said shunts, said shunts being so proportioned and said points so positioned thereon that bias potential controlled by the current in said receiving electrode is supplied between the control electrode and athode of said picture reproducing device from aid shunts, and means effective upon energization of said receiver to maintain the connection of said other shunt to the negative terminal of said source interrupted for a predetermined period, whereby the cathode of said reproducing device is positive with respect to said control electrode during said period, and thereafter to complete' said connection whereby the cathode of said reproducing device attains a value near the potential of the cathode of said amplifier.

11. The combination, in a television receiver, of an amplifier having a cathode and an electron receiving electrode, a picture reproducing device having a cathode, a control electrode, and an anode, a source of potential connected between said cathode of said amplifier and said anode of said picture reproducing device, two shunts across said source, said electron-receiving electrode and control electrode being connected to intermediate points on one of said shunts and said cathode of said reproducing device being connected to low potential point on the other of said shunts, said shunts being so proportioned and said points so positioned thereon that bias potential controlled by current in said receiving electrode is supplied between the control electrode and cathode of said picture reproducing device from said shunts, said other I thereby, and means to energize said heater upon energization 01 said receiver, said heater requiring a predetermined time to heat said cathode sufllciently to render said diode conductive, whereupon the potential of said cathode of said reproducing device is reduced from a value positive with respect to the potential of said control electrode to a value near the potential of the cathode of said amplifier.

RDBERT B. DOME. 

